1. Field of the Invention
The present invention relates to a signal input device and, more specifically, to a signal input device in which the conducting track unit is arranged on the shell by printing, eliminating the arrangement of conducting track unit bearing means.
2. Description of the Related Art
FIG. 1 illustrates a signal input device according to the prior art, which comprises a top cover 10a, a set of key buttons 20a, a set of rubber domes 31a, conductive contacts 40a, a printed circuit board 50a, a membrane circuit board 60a, and a bottom shell 70a. The top cover 10a has a plurality of through holes 11a. The key buttons 20a are axially and movably mounted in the through holes 11a. The conductive contacts 40a are respectively mounted in the rubber domes 31a on the bottom side. The printed circuit board 50a comprises an IC chip 51a. The top cover 10a, the membrane circuit board 60a and the bottom shell 70a are fastened together in proper order. The printed circuit board 50a is mounted in between the top cover 10a and the bottom shell 70a, and electrically connected to the membrane circuit board 60a. The rubber domes 31a are provided between the top cover 10a and the membrane circuit board 60a. The key buttons 20a are respectively aimed at the rubber domes 31a. The conductive contacts 40a are respectively disposed in the rubber domes 31a and facing the lead wires 61a of the membrane circuit board 60a. When pressing the key buttons 20a, the corresponding rubber domes 31a are depressed to force the respective conductive contacts 40a into contact with the corresponding lead wires 61a of the membrane circuit 60a, thereby causing the IC chip 51a to output a signal.
This structure of signal input device has numerous drawbacks as follows:    1. The signal input device comprises many components, resulting in a complicated assembly process and high manufacturing cost.    2. The connection between the membrane circuit board and the printed circuit board requires a special manufacturing process, increasing the processing time of the signal input device.    3. A locating means must be provided in the top cover and bottom shell of the signal input device for the positioning of the printed circuit board and the membrane circuit board, increasing the material consumption and processing cost of the signal input device.
Therefore, it is desirable to provide a signal input device that eliminates the aforesaid drawbacks.